{"id":237,"date":"2010-10-10T14:25:18","date_gmt":"2010-10-10T12:25:18","guid":{"rendered":"http:\/\/wordpress.callac.online\/index.php\/lecture-et-ecriture-dans-un-fichier-en-python\/"},"modified":"2022-01-05T22:41:54","modified_gmt":"2022-01-05T21:41:54","slug":"lecture-et-ecriture-dans-un-fichier-en-python","status":"publish","type":"page","link":"https:\/\/wordpress.callac.online\/index.php\/python\/generalites-sur-python\/lecture-et-ecriture-dans-un-fichier-en-python\/","title":{"rendered":"Lecture et \u00e9criture dans un fichier (en Python)"},"content":{"rendered":"

Pourquoi faire ?<\/h2>\n
\n

En programmation, il est souvent utile de s\u00e9parer le fichier contenant le programme des fichiers contenant des donn\u00e9es utiles au programme. Ces fichiers peuvent servir comme donn\u00e9es initiales mais aussi comme r\u00e9sultats du programme.<\/p>\n

C’est pourquoi, il est tr\u00e8s important de pouvoir manipuler les fichiers de texte par des commandes Python.<\/p>\n

Cr\u00e9ation d’un fichier de r\u00e9sultat<\/h2>\n
\n

Voici un exemple d’utilisation :<\/p>\n

# -*- coding:utf-8 -*-\n\nfichier1=open('monfichier.txt','w')\nfichier1.write(\"n\" +\"\\t\"+\"n^2\"+\"\\n\")\nfor i in range(10):\n    fichier1.write(str(i) +\"\\t\"+str(i**2)+\"\\n\")\nfichier1.close()<\/pre>\n
La lettre w<\/em> signifie que le fichier est ouverte en \u00e9criture. Cela a deux cons\u00e9quences capitales \u00e0 retenir :
\n– si le fichier monfichier.txt<\/em> n’existe pas, celui-ci est cr\u00e9\u00e9<\/strong>.
\n– si le fichier monfichier.txt<\/em> existe d\u00e9j\u00e0, celui-ci est effac\u00e9<\/strong> : toutes ses donn\u00e9es actuelles seront perdues.<\/p>\n
Utilisation d’un fichier de donn\u00e9es<\/h2>\n
\n
Reprenons le fichier pr\u00e9c\u00e9demment cr\u00e9\u00e9 pour sa lecture compl\u00e8te :<\/p>\n
fichier2=open('monfichier.txt','r')\nprint fichier2.read()\nfichier2.close()<\/pre>\n
qui renvoie comme r\u00e9sultat<\/p>\n
>>>
\nn n^2
\n0 0
\n1 1
\n2 4
\n3 9
\n4 16
\n5 25
\n6 36
\n7 49
\n8 64
\n9 81<\/p>\n
La lettre r<\/em> signifie que le fichier est ouverte en lecture.<\/p>\n
La commande read()<\/em> peut prendre comme argument un nombre d\u00e9signant le nombre de caract\u00e8res \u00e0 lire \u00e0 partir de la position courante. Ceci peut servir dans le cas du traitement par blocs des fichiers de grandes tailles.<\/p>\n
On peut aussi pr\u00e9f\u00e9rer une lecture par ligne en utilisant la commande readline()<\/em>.<\/p>\n
Pour en savoir plus, voici quelques lignes :
\n– version anglaise<\/a>
\n– version fran\u00e7aise<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"
Pourquoi faire ? En programmation, il est souvent utile de s\u00e9parer le fichier contenant le programme des fichiers contenant des donn\u00e9es utiles au programme. Ces fichiers peuvent servir comme donn\u00e9es…<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":1649,"menu_order":9,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-237","page","type-page","status-publish","hentry"],"yoast_head":"\nLecture et \u00e9criture dans un fichier (en Python) - Maths & Num\u00e9rique<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/wordpress.callac.online\/index.php\/python\/generalites-sur-python\/lecture-et-ecriture-dans-un-fichier-en-python\/\" \/>\n<meta property=\"og:locale\" content=\"fr_FR\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Lecture et \u00e9criture dans un fichier (en Python) - Maths & Num\u00e9rique\" \/>\n<meta property=\"og:description\" content=\"Pourquoi faire ? En programmation, il est souvent utile de s\u00e9parer le fichier contenant le programme des fichiers contenant des donn\u00e9es utiles au programme. 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